1. Field of the Invention
The invention relates to positioners operating by the principle of inertial motion.
2. Art Background
Positioners are in widespread use in many industrial and scientific applications. Applications which require the use of positioners include scanning probe microscopy, optical microscopy, Fourier transform spectrometry and semiconductor wafer handling.
One known type of positioner comprises a movable jockey comprising an extensible element connected at both ends to clamping elements which can be selectively actuated to clamp to and release from a reference rail or the like. In such positioners, motion is produced by clamping the first end, releasing the second end, extending the extensible element, clamping the second end, releasing the clamp at the first end, contracting the extensible element, clamping the first end, releasing the second end and so forth, thus generating motion in a wormlike fashion. Such positioners are known for example from U.S. Pat. No. 3,902,084, U.S. Pat. No. 4,874,979, U.S. Pat. No. 4,968,914 and U.S. Pat. No. 5,260,622.
Another type of positioner, this being the type of positioner to which the present invention relates, comprises two elements in frictional engagement with one another which slide relative to one another when the frictional force between them is overcome. Motion is generated by the interplay between inertia of one of the elements and slipping or sticking of the frictional engagement between the elements. Positioners of this kind are referred to as inertial positioners or slip-stick positioners and are known for example from an article by Dieter Pohl in the journal "Review of Scientific Instruments" in volume 58, pages 54 to 57 (1986) and further articles in the same journal in volume 59, pages 368 to 369 (1988) by Niedermann et al, volume 59, pages 1897 to 1902 (1988) by Lyding et al and volume 65, pages 2849 to 2852 (1994) by Wildoer et al, as well as from an article in the journal "Surface Science" by Anders et al in volume 181, pages 176 to 182 (1987).
Inertial slip-stick positioners can be made with only a few major components and can be driven with a single electrical signal, such as a sawtooth waveform. However, known inertial slip-stick positioners have a low load bearing capacity and a high degree of sensitivity to orientation, unlike the above-described worm positioners.